In digital television systems or services, such as those compliant with the ATSC Digital Television Standard and/or MPEG-2 protocols, tables containing various program and system information form part of the transport stream. One such table is a “virtual channel table” (in ATSC nomenclature), also known as a channel map. This channel map provides information regarding major and minor channel numbers, carrier frequencies, program numbers and other useful information for all of the virtual channels supported by the system. The virtual channel table syntax includes a “current_next_indicator,” which indicates whether the channel map being provided is currently valid or will become valid “next” (i.e. once the currently valid channel map is no longer valid). Other program and system information tables also include a “current_next_indicator.”
When a channel map or other table is to be valid “next,” the receiver cannot anticipate when the table will become “current.” As a result, when the table becomes “current,” it must be processed immediately in real time by the receiver. In order for channel map changes and other table changes to be reflected quickly at the receiver, the tables must be transmitted in the transport stream as frequently as possible, consuming valuable bandwidth in the transport stream. For channel maps in particular, this problem becomes more significant as increasing numbers of channels must be described in the channel maps. The channel maps must be transmitted along with a large amount of other program data such as program titles, descriptions, schedules, categories and ratings, as well as the packetized elementary streams containing audio and video data, all of which compete for the limited available bandwidth.